What’s Up With That: My Beer Tastes Like a Skunk’s Bathwater

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I like beer, and I ain’t picky. In fact, I go out of my way to try new brews. I’ve explored hop-laden IPAs, cheek-puckering sours, gruits brewed with lichen, and I still appreciate a Budweiser. The only beer I can’t abide is one that fills my mouth with bunk-ass, skunky flavor.

You know what I’m talking about. You crack a bottle, take a swig, and your mouth is filled with what tastes like a skunk’s bath water. I wanted to know what causes the funky flavor, and more importantly, can it be stopped?

What's Up With That?

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Granted, light has ruined many a buzz (Closing time already!?!), but how does light turn my favorite drink into a something I can’t stand?

It’s best to start with a bit of background on brewing, says Barth. Beer begins with malted grains (usually barley, but rice, corn, wheat, rye, and oats also are used), which are stewed in hot water until their starches break down into dissolvable sugars. Remove the spent grains, then boil in the hops. This releases from the hops a ring-shaped molecule called isohumulone, which is responsible for beer’s characteristic bitterness. The final step is adding yeast, which converts the malty sugars into alcohol. But let’s get back to those beautiful, bitter isohumulones, because those are where light does its dirty work.

Ultraviolet rays break the bond connecting the central isohumulone ring to a side chain of oxygen and carbon molecules. This newly released molecule (called a free radical) has a spare electron, which is desperate to bond with any other available molecule. Floating in the beer are many potential partners, most of which are safe from a taste perspective. However, when a free radical mingles with a certain sulfur alcohol molecule (called sulfmethyl) present in small amounts in beer, the two will combine into something that smells a lot like an angry skunk.

In fact, Barth says the molecule they create, 3-methylbut-2-ene-1-thiol (or 3MBT), is similar to the chemical responsible for the skunk’s stink. It doesn’t take much to spoil your brew, either. According to Barth, your tongue can taste 3MBTs at a concentration of seven parts per trillion. This would be like tasting a pint glass of beer poured into a large pond (please don’t attempt this).

Clear glass bottles leave your beer the most vulnerable. Green bottles offer some protection, but not enough to mount an argument in their defense. However, there is a cure: Brown bottles block the ultraviolet rays that break isohumulones apart, which is why most craft brewers always have chosen brown glass. Until recently, that is. Many brewers are switching to aluminum cans, which have some advantages over bottles and can also keep beer from being lightstruck.

But if your beer isn’t in a can or a brown bottle, it doesn’t take much light to start the skunking. “If you carry a beer into the bright sun, it can get skunked almost immediately,” Barth said. Fluorescent lights will do the job in a matter of hours. More hops means more isohumulones, so the hoppier the beer, the faster and more thorough the skunk.

This could explain why certain clear-bottled brands suggest you squeeze a lime into their beer to mask the skunk before taking a swig. But if you must, for reasons I will never understand, drink a Heineken, I suggest you get it on tap and hide your shame in a dark corner of the bar.